Message-ID: <49CBA5DE.6050206@microgate.com>
Date: Thu, 26 Mar 2009 09:57:18 -0600
From: Paul Fulghum <paulkf@microgate.com>
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To: Paul Rolland <rol@as2917.net>
CC: linux-kernel@vger.kernel.org
Subject: Re: Linux 2.6.x - Serial port signalling not maintained when closing
 device
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Paul Rolland wrote:
> I'm using small devices that are connected on the serial port, and powered
> using RTS and DTR.
> When using kernel 2.4.x (at least 2.4.31), I could easily control the
> powering of the device using :
>  stty -F /dev/ttyS0 ospeed 9600 (this would put RTS and DTR to 1 / power)
> and
>  stty -F /dev/ttyS0 ospeed 0 (this would turn it off).
> 
> I've recently updated one of the machine to a new 2.6.29 kernel, and this
> is not working anymore.
> As far as I can see, I need to have an application that keeps /dev/ttyS0
> open for this to work. As soon as no application is using the port,
> everything goes down again.

Are you explicitly clearing the HUPCL flag?
(stty -F /dev/ttyS0 -hupcl)

I just did a quick test on 2.6.22 and DTR/RTS are maintained
with your commands above, but only after clearing HUPCL.

-- 
Paul Fulghum
MicroGate Systems, Ltd.
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